| The terahertz detector and emitter are necessary devices in the terahertz technology.Terahertz source is the cornerstone,how to represent and control is the key.Therefore,in the process of studying terahertz emitter,we are also dedicated to the study of terahertz detector.How to effectively coupling the radiation from free space into a tunnel junction is a crucial issue in practical applications.At higher frequencies,the admittance of the junction capacitance grows but meanwhile the backshort will inevitably suffer increasing losses which reduce the effectiveness of the coupling,so it is essential to provide a circuit for tuning out this capacitance at the operating frequency.This method can improve the coupling efficiency and sensitivity of the superconducting Josephson terahertz detector.In the process of studying superconducting THz detectors,we found that the self-mixing phenomenon of superconducting Josephson junction array.High temperature superconductor(HTS)Bi2Sr2CaCu2O8(BSCCO)IJJs(intrinsic Josephson junction)contain as many as thousands of independent units due to its multilayer physical structure.This provide abundant information for the mixing signal,which can fully reflect the radiation properties of superconducting Josephson junction array.Furthermore,the discovery of the new Josephson junction in superconducting material is a long and rewarding work.This paper aims to study the performance improvement method of terahertz detector,self-mixing detection technology of superconducting Josephson junction array,and explore the characteristics of new type of Josephson junction.The main contents are described as follows:Firstly,the poor signal transmission efficiency always caused by Josephson junction capacitance in superconducting Josephson detectors.Thus,we described a method to tune out the capacitance and realize impedance matching within the range of 400-500GHz for SIS detector with the Nb/AlOx/Nb tunnel junctions.This method can be applied to improving the performance of other Josephson detectors.Secondly,we studied the performance of HTS BSCCO detector.By designing the matching network and tuning structure,the coupling efficiency and sensitivity of the signal were improved.In addition,we designed the integrated structure of HTS radiation source and detector,which provided the possibility argument for further implementation.Thirdly,we studied the self-mixing detection technology of HTS BSCCO radiation source by measuring different typical samples.We found that,at low bath temperatures,in the low-bias regime the terahertz emission(although showing only a single peak)was accompanied with noisy IF spectra,sometimes exhibiting several peaks.This indicated that groups of junctions oscillated at different frequencies.By contrast,in the high-bias regime,the IF spectra were near the background level.Experimental results showed that due to the appearance of hotspot,the phase consistency of the IJJs involved in the radiation were better.The study not only provided a more convenient and effective detection method,but also provided a further supplement to the radiation mechanism of HTS BSCCO emitter.Finally,in order to further explore the new Josephson junction,we studied the grain boundaries within mechanically formed polycrystalline Ba0.6K0.4Fe2As2 micro-bridges.By tunneling current across grain boundaries,current-voltage characteristics(IVCs)demonstrated the typical Josephson weak links behavior in micro-bridges.The current-voltage characteristic curve can reflect the current characteristic of Josephson tunneling of superconductor-normal metal-superconductor.Meanwhile,Shapiro steps were observed under the microwave radiation at 10 GHz.By comparing the relationship between measured and numerical temperature dependence of the critical current,the pairing mechanism was analyzed.These were complementary to the material properties of new Josephson junction. |
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